1. Field of the Invention
The present invention relates to a safety cap system with an external locking and unlocking element for an automotive cooling device, to prevent premature unlocking of the safety cap under abnormal pressure and temperature conditions. The present invention specifically relates to a safety cap with a torque overriding arrangement and a pressure and temperature controlled sensor to provide an effective locking and unlocking of the safety cap and a method thereof.
2. Description of the Background Art
With the advent of engines with increased horsepower, smaller radiators and higher thermostat opening temperatures, much more heat is accumulated in the engines of cars and other vehicles of today. These vehicles include trucks, LCVs, MCVs, vans, cars, snowmobiles, marine engines, off-road vehicles and sport utility vehicles. These vehicles have less engine surface to dissipate the heat into the atmosphere than older type of engines. To contain the excess heat build-up problem, the pressurized cooling system was developed. The radiator or any other safety-caps in these pressurized systems function to provide a safe opening so that liquid or any other suitable medium can be vented out and to maintain the desired system pressure.
Pressurized vessels are often provided with a closure cap or a valve which, when removed, allows the tank to release pressure and be filled with refilling coolant.
However, the premature removal of the closure cap subsequent to the pressurized vessel involves a sudden release of pressure when the cap is removed. This sudden release of pressure creates a dangerous situation resulting in expulsion of some liquid and steam from within the tank.
During operation, when an engine becomes very hot, the engine cooling fluid can reach a temperature as high as 118 to 129° C. and pressure levels as high as 110–117 kPa. (USA-NHTSA—Federal Register Vol 66 No.108 Jun. 1, 2001/Proposed rules). Under such high temperature and pressure conditions, the sudden release of pressure upon removal of the closure cap, subsequent to the pressurization of the reservoir is also dangerous to the effect that it may result in the cap of the cooling device getting blown off. In effect, the cap may become a dangerous projectile or a missile, thereby exposing the persons in the vicinity to the threat of serious bodily injuries, should the cap blow off the cooling device during the unscrewing operation and also spraying the persons close to the cooling device with the hot fluid or steam that is ejected.
Some of the conventional pressure cap units are so designed that once the pressure increases in the system it is capable of being removed when the cooling device is in hot condition. Under this condition the user is exposed to the risk of being injured by the highly pressurized cap and getting scalded from the steam jet that emerges out of the cooling device.
There have been numerous instances where the high-pressure steam or hot liquid is ejected out from the engine cooling system during cap removal process, thereby causing serious bodily injuries.
U.S. Pat. No. 4,927,049 teaches an internal thermally locking radiator cap for fitting on the filler neck flange of an automotive radiator, which prevents the radiator cap from becoming detached from the filler neck flange when the radiator is hot. The cap uses a bi-metallic strip captured on the top surface of the radiator cap and having an end that goes through the opening of the radiator cap and engages the filler neck flange to lock the cap in place.
U.S. Pat. No. 5,042,677 discloses a radiator cap with a safety plate or wire made of memory alloy. The safety plate or wire bends downward under ambient temperature. High temperature water in the radiator causes the safety plate to extend out due to the memory characteristic of the alloy and the safety plate thus presses against the neck of the filling hole.
One such provision to remove the excess pressure conditions before the cap is removed completely was disclosed in U.S. Pat. No. 5,603,425, wherein a radiator cap with sealing members is disclosed. However, the product covered under the above said patent has the following limitation that a user of this cap, while closing the cap, does not seem to receive any feedback to indicate that the cap has reached its desired torque limit; as result the cap can be tightened below the desired limits resulting in high installation torque and high removal of torque further leading to inconvenience to the operator using the cap. The tightening of the cap may result in improper seating of the small o-ring, which further leads to ineffective sealing thereby leading to pressure and coolant loss.
U.S. Pat. No. 6,378,717 discloses a closure cap without a ratcheting with an internal locking means with a temperature controlled element to prevent unscrewing of the cap when the heat in the reservoir is in excess levels. Further, an exclusive and special reservoir is required for the closure cap of this design. In addition, the instant design may not be adaptable to radiator application because of lack of controlled vent path and also due to loss of coolant.
In addition, closure caps of an engine cooling device, functioning on the basis of temperature sensing can fail to actuate the sensor if an end user tries to locally cool the cap by pouring cold water on the heated cap or the cap may fail to cooperate if a snow falls on the cap when the hood is kept opened for cooling.